Patent GB-706446-A (GB)
Title: Process for the selective catalytic cracking of hydrocarbon oils
IPC: C10G11/04
Filed: 1951-11-21
Abstract: <PICT:0706446/III/1> In a process for the selective catalytic cracking of hydrocarbon oils, the oil is subjected to preliminary thermal cracking and the products therefrom are flash distilled to separate two distillates boiling above gasoline, which are submitted separately to catalytic cracking.  The higher boiling distillate is catalytically cracked at a higher temperature and for a shorter time than the lower boiling distillate.  The products from the two catalytic cracking zones are passed to a fractionation zone, from which gasoline and gas oil are withdrawn as final products, while two fractions boiling above gas oil are withdrawn for recycling. The lower boiling of these two fractions is recycled to the catalytic cracking zone of lower temperature, and the higher boiling fraction is recycled to the thermal cracking zone.  Crude oil residue boiling above 315 DEG  C. is fed through line 1 into thermal cracking furnace 2, where it is heated to 480 DEG C. at a gauge pressure of 2 atm. The products are flash distilled at atmospheric pressure in chamber 3.  The vapours from chamber 3 are passed to dephlegmator 5, from which gases and gasoline are withdrawn overhead, and a fraction boiling between 260 DEG  and 480 DEG C. is withdrawn as bottoms. This fraction is passed through lines 35 and 37 to heater 23 wherein it is heated to 425 DEG C.; and it is then introduced through line 38 into reactor 27 which contains a dense bed of fluidized catalyst 30. The temperature in reactor 27 is 480 DEG C., and the rate of throughput is 0.2 to 0.1 kg./hour/kg. catalyst.  The reaction time can be regulated by means of the height of the catalyst bed.  The residue obtained in flash chamber 3 is fed to flash chamber 13, which is maintained at a pressure of 30 mm. by steam ejector 20.  A pitchlike residue is discharged from chamber 13 through line 14.  The vapours evolved in chamber 13 are condensed, and the condensate is collected in receiver 18. This distillate is passed through line 21 to heater 23 wherein it is raised to 370 DEG C., and is then contacted in tube 24 with hot catalyst at 590 DEG  C., which is supplied from regenerator 26 via standpipe 25.  Tube 24 comprises the cracking zone for the heavier distillate; the period of contact is governed by the diameter of the tube, and may be regulated by supply of steam through line 28. The temperature in tube 24 is 515 DEG C., and the rate of throughput is 2 to 20 kg./hour/kg. catalyst.  The mixture of catalyst and vapours from tube 24 discharges into reactor 27.  The vapours escape upwards, but the catalyst is diverted by deflector cap 29 to catalyst bed 30.  The components absorbed on the catalyst are cracked in bed 30.  Catalyst is withdrawn from bed 30 through line 31, and is passed to stripper 32 werein it is treated with steam. Oil vapours and steam are passed from stripper 32 to reactor 27 through line 34.  Vapours are discharged from reactor 27 through cyclones (not shown), and are passed through line 39 to fractionating column 40, which is operated at a gauge pressure of 1.35 atm.  The temperature at the top of column 40 is maintained at 205 DEG C. by pumping round a fraction through line 46 and cooler 47. Gases and gasoline vapours are withdrawn from the head of the column, and passed to cooler 42.  Gasoline is separated from gases in separator 43.  A gas oil fraction is discharged from column 40 through line 48, and is stripped of higher components in stripper 49. Gas oil boiling between 205 DEG  and 370 DEG C. is removed through line 51.  A fraction from column 40 boiling between 315 DEG  and 540 DEG C. is introduced into line 37 via line 54; and is then cracked in reactor 27.  The temperature in the lowest part of column 40 is maintained at 370 DEG  by circulating part of the highest boiling components via line 56, pump 57, cooler 58 and line 59. The remaining part of the oil discharged through line 56 is fed by pump 60 to supply line 1.  The stripped catalyst is passed from stripper 32 to regenerator 26, which is supplied with air through lines 61 and 62. The temperature in the regenerator is adjusted by circulating catalyst through cooler 64 by the air supplied through line 62.